The present invention relates to methods and apparatus for ink jet printing and, more particularly, to methods and apparatus for ink jet printing which apply drying air to a printed substrate.
The present invention is directed to improvements in methods of ink jet printing. Those skilled in the art will appreciate that ink jet printers typically comprise an ink jet having a plurality of ink nozzles which propel, i.e., print, ink onto a substrate spaced a slight distance from the ink jet nozzles. Many modern ink jet printers comprise reciprocating print heads and mechanisms for driving the substrate. The print head is typically reciprocated along an axis perpendicular to the direction of travel of the substrate.
It is generally desirable to print clearly and quickly, however, these two parameters are often conflicting since the quicker the printing process proceeds, the less time that the printed ink will have to set, i.e., sufficiently dry, prior to the next pass of the print head in order to prevent puddling or bleeding of the ink droplets. If the ink droplets from previous passes has not yet set sufficiently on the substrate, then the application of successive rows of ink droplets will tend to cause puddling, bleeding and resultant image distortion. Therefore, it is desirable to have printed ink droplets sufficiently set prior to subsequent passes of the print head.
Previous devices have disclosed various methods for drying printed substrates. For example, some prior art devices apply heat to one or more drums over which a substrate passes after it has been printed. Other devices direct heated air onto the printed substrate. One disadvantage of applying heated air in the vicinity of the print head is that the heat tends to clog the ink jet nozzles. Therefore, while hot air accelerates ink drying on the substrate, it also accelerates ink drying on the print head ink jet nozzles which can then tend to become clogged with dried ink.
It would therefore be desirable to provide a system for rapidly drying a printed substrate a very short time after each printing pass of a print head while minimizing the deleterious effects of applying heat to the ink jet nozzles.
The various embodiments of the present invention are directed to apparatus and methods for applying drying air to a printed substrate during each pass of a print head over the substrate. Preferred embodiments of the present invention direct heated air onto the printed substrate and then draw that heated air away from the proximity of the substrate with a vacuum.
One preferred embodiment of the present invention comprises a heated air nozzle, preferably comprising a plurality of elongated hot air outlets, all of which are substantially surrounded by a vacuum. This drying head is advantageously mounted on or in tandem with a reciprocating print head such that heated air is first directed onto the printed substrate and then immediately drawn away from the substrate with a vacuum during each pass of the reciprocating print head.
One advantage of the embodiments of the present invention is that they enable the use of slower drying inks than would otherwise be employed for a particular printing process.